Specifications include, but are not limited to: In each location as detailed above, the existing culverts will be excavated, removed, and disposed of by the contractor. Existing backfill will be removed from the trench excavation site by the contractor. Trench bottoms containing bedrock, soft muck, refuse, or other material unable to provide long-term uniform pipe support are unacceptable. All unsuitable foundation materials should be excavated before the new culvert pipe installation proceeds. The contractor should remove rock or unyielding material 1-foot below grade and 6 inches on either side of pipe. Soft areas within the foundation should be removed approximately 2 feet below grade and three times pipe width. A synthetic fabric (geotextile) will be required to separate native soil from backfill material. Excavation will occur at each culvert location using the lines and grades of the existing culverts unless final cover depth requirements or site conditions dictate adjustments be made. Minimum trench cover depth and width requirements for the new 18-inch culvert pipe will be as shown on the Trench Installation Detail in Attachment No.1.
